1. Field of the Invention
This invention relates to electromagnetic devices and, more particularly, to electromagnetic devices having independently coupled inductive components, such as inductors or transformers.
2. Description of the Prior Art
Electromagnetic devices have been used in a wide variety of applications, such as power supplies, etc. These devices generally comprise a magnetic core and one or more windings. Some power supplies use multiple electromagnetic devices at various stages of their power conversion circuitry. Conventionally, the magnetic cores of multiple electromagnetic devices has been integrated to increase the power density and decrease the component count of some power supplies. For example, known power conversion circuitry have used an integrated magnetic core to achieve magnetic coupling between two filter inductors. An integrated magnetic core is also used for magnetically coupling a filter inductor and a resonant inductor in switching power supplies. In these known approaches, however, the voltage waveforms across the magnetically coupled inductors are proportional to each other.
In some applications, it is desired that the voltage waveforms across the windings not to be proportional. FIG. 1 shows a known multi-port electromagnetic device that couples two windings in this manner. However, under this arrangement, one winding of the multi-port electromagnetic device of FIG. 1 is significantly influenced by the applied voltage across the other winding. In other words, the two windings of the multi-port electromagnetic device of FIG. 1 are dependent on each other because of their mutual inductance.
In some applications, it is necessary to provide a multi-port electromagnetic device having independent windings, for example, in power supplies that have multiple converter stages, where the inductive components in various stages should be independent of each other. This requirement makes the multi-port electromagnetic device of FIG. 1 unsuitable for such power supplies because of its dependent inductive components.
FIG. 2 shown another known multi-port electromagnetic device that uses a pair of E-shaped magnetic cores with symmetrical and asymmetrical windings to provide independent inductive components. However, in the multi-port electromagnetic device of FIG. 2, the reluctances of the two outer legs of the E core must be identical. Otherwise, if the reluctances of the two outer legs of the E-shaped cores are different from each other, the magnetic flux generated by the winding on the middle leg is not equally distributed to the outer legs. Consequently, the induced voltage across the windings of the outer legs are significantly influenced by the voltage across the winding on the inner leg, which causes the two windings not to be magnetically independent of each other.
Therefore, there exists a need for a compact multi-port electromagnetic device that has windings that are inductively independent of each other.